Process for the electrolytic manufacture of perborates.



UNIT STATES PATENT OFFICE.

KURT ARNIDT, 0F CHARLOTTENBUBG', GERMANY, ASSIGNOIR, TO THE CHEMISCHE FABRIK GRUNAU LANDSHOFLE' AND MEYEB AKTIEXGESELLSQHAFT, OF GRUNAU,

NEAR BERLIN, GERMANY.

PROCESS FOR THE ELECTROLYTIC MANUFACTURE OF PEREORATES.

No Erawing.

To all whom it may concern:

Be it known that I, KURT Armor, a subject of .the German Emperor, residing at Charlottenburg, Germany, have invented a certain new and useful Process forthe Electrolytic. Manufacture of Perborates, of which the following is a specification.

Hitherto the electrolytic manufacture of perborates by means of direct currents has not been found practicable.

l have tried to increase the conductivity of saturated borate-solution by means of suitable additions, for instance by adding a carbonate to such a solution, and to my surprise I discovered, that in electrolyzing such a mixture of carbonate and borate by means of a continuous current, abundant quantities of persalt are formed at the temperature of a living room.

If a saturated aqueous solution of sodiumtetra-borate is electrolyzed by means of platinum-electrodes (with a current of 0.8 amperes and 16 volts) while under cooling, no perborate is formed. Even if the conductivity of the electrolyte is increased by the addition of (caustic) soda solution or sodium sulfate, a distinct smell of ozone occurs, but no perborate is produced, either in alkaline or acid solution. Even the easily soluble potassium-borate, whose concentrated solution conducts the current very easily, did not yield any persalt, when-elec trolyzed (2 amperes and 8 volts). A sample of 2 cubic centimeters taken after the elec-- trolysis had continued for a quarter of an hour, was subjected to the usual quantitive test and was found to decolorize only very slowly 3 drops of a permanganate solution, 1 cubic centimeter of which corresponded with 1.06 milligrams of active oxygen. The strong ozone smell of the electrolyte suggested, that this minute and remarkably slow consumption of permanganate was due to the ozone arising from the electrolysis; As soon, however, as a larger quantity of potassium-carbonate had been introduced into the same potassium-borat-e solution, the electrolysis immediately yielded the persalt, while no ozone was perceptible by its smell. After the electrolysis had lasted 1% hours, the electrolyte already contained 6-3,- gramsof active oxygen per liter. If, on the other hand, a carbonate solution is electrolyzed at ordinary temperature without Specification of Letters Patent.

Patented Dec. 9, 1913.

Application filed December 30, 1912. Serial No. 739,369.

the addition of borate or boric acid, some percarbonate is obtained in the solution, but the formation of persalt is very minute, because the major part of the pcrcarl'iouatc formed on the anode is split up again into carbonate and oxygen during the electrolysis. After the electrolysis the solution yields continually an abundance of gas, and after some time active oxygen is no longer perceptible. In contradistinction to this the solution consisting of carbonate and borate does not yield any considerable quantities of gas after the electrolysis, and when allowed to stand for several days, it still contains undecomposed the persalt which has been formed.

On the base of the results of the above experiments it is now possible to produce perborates, and in particular the sodium perborate, by electrolyzing aqueous solutions consisting of a mixture of sodium-carbonate and borax. It is advantageous to use concentrated solutions of alkalicarbonate and borate, in order that the electro current re= quired for a given quantity of perborate may be as small as possible. For instance,

150 grams of sodium carbonate and 60 grams of borax may be employed to 1 liter of water. The sodium perborate is so little soluble in a solution containing 150 grams of sodiuincarbonate and 60 grams of borax in 1000 cubic centimeters that in the case of a stronglysupersaturated perboratesolution easily obtained by electrolysis, the major part of the perborate will afterward crystallize out. Consequently, very slight cooling below the temperature of a living room is sufficient for causing the sodium perborate to separate out and it is possible by a suitable arrangement of a receptacle suitable for electrolyzation and one suitable for crystallization, and of the electrolyte circulating between the two receptacles, to cause a continuous electrolytic separation'of the sodium perborate from the electrolyte solution. It is not necessary to separate the anode from the cathode by a porous partition.

hat I claim is 1. The process for the electrolytic manu facture of perborates from a borate solution, which consists in electrolyzing a borate so lution to which has been added a soluble carbonate, substantially as described.

2. The process for the electrolytic manu v In testlmony whereof I have hereunto set my hand in presence of two subscribing witnesses.

3. KURT ARNDT.

Witnesses ADOLF MIETLY, BRUNO SEEGERT. 

